Description of the Prior Art
This invention relates to a printing device which can be mounted on a portable label printing and applying machine, a price tag printing and attaching machine, or the like.
More particularly, the invention relates to a printing device in which a plurality of type wheels are arranged side-by-side on a common axis and a plurality of indicating wheels, each corresponding to, paired with and in engagement with a respective type wheel, are arranged side-by-side on a second common axis. The arrays of type and indicating wheels are supported in the space between a frame comprised of a pair of side frames. An indexing shaft, having a selector knob projecting from one of the side frames, extends along the direction of the aligned axes of the indicating wheels. The indexing shaft is slid along the axes of the indicating wheels so as to select and engage a particular indicating wheel. Upon rotation of the indexing shaft, the selected indicating wheel and the corresponding type wheel are rotated to a particular print position.
Many devices of the described type are in use. See, for example, U.S. application Ser. No. 658,491, filed Feb. 17, 1976 and 678,761, filed Apr. 21, 1976. One example of such a printing device from the prior art is described in the description below of a preferred embodiment.
In one prior arrangement, the indexing shaft passes through a supporting sleeve. The shaft has a pinion attached on it. The teeth of the pinion engage and rotate each selected indicating wheel. The supporting sleeve has axial grooves to permit the pinion teeth to project through and to engage the indicating wheels. Necessarily, the rotation of the indexing shaft correspondingly rotates the sleeve through which the pinion teeth project.
Forming the sleeve to be strong enough to support the shaft limits the number of axial grooves the sleeve may have. This, in turn, limits the number of teeth on the pinion. A smaller number of teeth are each under greater stress and are more likely to be damaged through use. Also, axial shifting of the indexing shaft through the indicating wheels to bring the pinion to a particular indicating wheel is inhibited by friction between the indexing shaft and the sleeve. Further, rotation of the indexing shaft to rotate the pinion together with the sleeve is inhibited because the sleeve rubs and is frictionally retarded by its contact with all of the indicating wheels not then being rotated by the pinion.
Once the indexing shaft has been rotated to rotate the pinion and the corresponding indicating wheel, the shaft and its operating knob are projecting out of the side frame. Especially when the indicating wheel that has been rotated is near to the side frame from which the indexing shaft projects, the shaft is projecting out quite far and is liable to be bent or damaged by or to cause damage by contacting other objects, by the labeler being dropped, etc. It is desirable to shift the shaft away from such a vulnerable position.
In order to avoid the above mentioned problem, operators must always move the indexing shaft and its knob fully into the printing device by axially pushing the selector knob into the printing device after completion of type selection. However, operators often forget to push in the selector knob and thus the projecting indexing shaft is sometimes damaged.